The present invention relates to containers or vessels used to hold and ship specialty and other materials such as high-purity (HP) and ultra-high-purity (UHP) fluids.
New developments and enhancements in technologies utilized in the electronics industry are leading to demands for increasing quantities of specialty materials such as HP and UHP fluids used in manufacturing processes. Specialty materials are chemicals used in manufacturing processes, such as the manufacture of electronic components, that exhibit certain properties such as high purity or ultra high purity. Specialty materials can be, for example, powders, emulsions, suspensions, and vapors. The term “fluids,” as used herein, is intended to encompass gases, liquids, sublimed solids, and combinations thereof.
Specialty materials used for different processes and treatment of associated production equipment may require delivery of products with impurities measured at the ppb level. Even though specialty gases and chemicals may account for only about 0.01 to about 0.1 percent of production expenses, a shortage of these materials can jeopardize the ability to maintain desired or required production volumes in, for example, electronics manufacturing facilities. In some cases, using contaminated product in a manufacturing process may jeopardize the final product specifications. The specifications of the final product may be determined at the very last stage of the manufacturing processes. For example, in the case of wafer production, the specifications of the final product may be checked during a product quality assurance procedure. Produced wafers may be considered “out of spec” and may be thrown away, which can account for the losses of many millions of dollars. Therefore, preserving the purity of specialty materials during delivery is of substantial importance.
Contamination of a vessel used to hold an HP or UHP fluid or other specialty material can be characterized as the presence of substances that can compromise a pre-defined purity level of the specialty material upon introduction of the specialty material into the vessel, or the penetration of the impurities into the vessel during transportation and/or storing of the high purity products in the vessel.
Contaminants can take the form of solids, liquids, and gases. Contaminants can be formed, for example, by residue from another type of material previously stored in the vessel. Contaminants can also be introduced by, for example, infiltration of ambient air into the internal volume of the vessel due to leaks in the vessel. More particularly, oxygen introduced by ambient-air infiltration is generally considered a contaminant with respect to HP and UHP fluids and other specialty materials used in the manufacture of electronics. The oxygen can form contaminating oxides on the interior surfaces of the vessel. Moreover, oxygen molecules can be trapped on the internal surfaces of the vessel, and can diffuse into the HP or UHP fluid or other specialty material which is subsequently placed in the vessel. As the HP or UHP fluid resides in a vessel, the oxygen molecules can be drawn out of the vessel internal surfaces due to a concentration gradient with the HP or UHP fluid and carried into the production facility, adversely affecting the final product specification.
Substances characterized as contaminants for a specialty material are application-dependent, and can vary with factors such as the specific type of specialty material, the product specification of the specialty material, and the intended use of the specialty material. Thus, a substance considered a contaminant in one application may not be considered a contaminant in other applications. For example, oxygen, hydrocarbons, metal particles, water, and nitrogen are considered contaminants of supercritical carbon dioxide (SCCO2). Nitrogen is not considered a contaminant, however, of electronics-grade gases such as NH3, NF3, and Cl2.
In some cases, the older delivery methods for delivering small quantities of HP and UHP materials may no longer be applicable. For example, deliveries using cylinder bottles or other small packages may no longer be acceptable in some manufacturing processes due to the need for relatively large quantities of such materials. For example, demands for ultra-high purity “White Ammonia” (NH3) and high purity nitrogen-triflouride (NF3) have grown significantly in recent years, and bulk quantities of these materials are now required in many different manufacturing processes.
Bulk delivery vessels and systems for delivering HP and UHP materials were not known or used in the recent past. Only the recent development of new technologies, for example, technologies used for production of various electronic devices, have lead to the demand for large quantities of HP and UHP products such as NF3, NH3, Cl2, HCl, and other specialty gases and chemicals. Small containers such as bottle cylinders were used in the past for delivery of relatively small quantities of HP and UHP products. Requirements for the preparation of small containers, while stringent, can be met relatively easily. Indeed, container preparation procedures for relatively small containers and vessels which are used to transport HP and UHP products are well known. For example, a simple container heating process in an oven, known as “baking,” helps to achieve the required purity of container internal surfaces. Prepared or so called “purity treated” containers may receive UHP products without the threat of contaminating the UHP products. “Baking” ovens used for container heating may vary in size and shape, but typically are restricted to the preparation of relatively small containers such as cylinders.
Large size containers or vessels, such as those necessary for the delivery of industrial gases in bulk quantities, cannot utilize the preparation methods for relatively small containers. New container preparation methods for bulk HP and UHP products have been developed and introduced to the container industry. For example, preparation of ISO containers of about 6,000-pound capacity is described in U.S. Pat. Nos. 6,616,769B2 and 6,814,092B2, titled “Systems and Methods for conditioning Ultra High Purity Gas Bulk Containers.” The preparation of these containers is much more complex than the preparation of smaller containers because the larger containers are too large to fit into existing “baking” ovens, and also because maximum surface temperature of the containers is regulated by national transportation bodies, agreements, and conventions including, for example, the U.S. Department of Transportation (DOT), the United Nations (UN), the International Maritime Dangerous Goods (IMDG), the European Agreement Concerning the Carriage of Dangerous Goods by Road (ADR), the Convention for Safe Containers (CSC), etc. In other words, large containers used as transport vessels are regulated by transportation organizations around the world. For example, according to DOT recommendations, the maximum outside temperature of a portable ISO tank T50 type should not exceed 125° F., to avoid introducing thermal stresses and fatigue in tank. Apparently, a “baking” process cannot be performed since baking requires significantly higher temperatures to achieve adequate container surface preparation.
Methods for cleaning and preparing large size vessels for delivery of HP and UHP products are known and are in practice in the industry. These methods are quite involved and require significant effort and expense. Therefore, preservation of container purity is essential, and may significantly influence both delivered HP or UHP product revenue and quality of the devices produced using the delivered HP or UHP materials. For example, various steps of the manufacturing process for semiconductor wafers may rely on the use of delivered HP and UHP substances such as NF3, NH3, CO2, etc.
Significant effort has been undertaken to develop and implement delivery systems and means for HP and UHP materials in bulk quantities. One of the important challenges associated with these deliveries has been the design and preparation of bulk containers in a way that these containers may be used to transport and deliver the required product purity without jeopardizing the latter. Some unique vessel designs and preparation procedures are known today. The task of container design and preparation to satisfy the handling of high purity substances is somewhat less complex in the case of stationary containers. For portable containers, however, the task of achieving and preserving product purity is more challenging. Portable containers need to comply with various regulations imposed not only by standards regulating container materials, design, and mechanical properties, but also by different national transportation bodies around the world including, for example, DOT, UN, IMDG, ADR, CSC, etc. The job of these bodies and their regulations is to make sure that portable containers carrying bulk quantities of different materials do not impose danger to the surrounding world during the transportation process. Container design, inspection, transportation, and other handling procedures are strictly regulated, and all containers that fail to comply with existing regulations are not permitted to be used for transporting dangerous goods. At the same time, some of the container design, preparation, and inspection procedures contradict high purity product requirements.
One would need to understand the requirements that are imposed on transportable containers to understand what may and may not be done to a standard container design, a regulated container preparation process, an inspection procedure, etc. New or modified container designs, as well as new or modified preparation and inspection procedures may need to be approved for use by national transportation bodies. An example of some of the inspection-related requirements imposed on containers is shown in the section “ISO Inspection Requirements” of ITCO ACC MANUAL issue No. 3: Jan. 2003, which states: “[f] or man entry it is the responsibility of depot supervisor to ensure that the tank is safe to enter. This may require an inspection for gas contamination of low oxygen.” This statement taken from the container inspection manual means that in the case of man entry to the tank (container), appropriate conditions are required to ensure that no hazardous gas residue is left inside the container, and the oxygen deficient atmosphere is eliminated. The latter may require an air purge if the container which may be a source of major container contamination forming, for example, metal oxides and other undesirable residue. In addition, a thorough container preparation (decontamination) procedure will be required to eliminate residual oxygen even after the container is purged with inert gas. Container surfaces may trap significant amount of oxygen which would be enough to contaminate a UHP product subsequently introduced into the container. An example of a quite involved container preparation method is described, for example, in U.S. Pat. No. 6,616,769B2. Thus, a substantial amount of time, energy, and money can be saved by avoiding the need for container preparations whenever possible.
Another example of regulated container inspection requirements may be found in chapter “Pressure Vessel Not Acceptable Conditions” of the ITCO ACC MANUAL issue No. 3: Jan. 2003. For example, the following vessel conditions found during the inspection may qualify the inspected vessel as unacceptable for further use:                defects to welds or parent materials        body executed grinding, deeper than 0.1 mm (0.004 inch)        Excessive grinding or other metal depletion which reduces the shell thickness to less than the minimum        Corrosion or pitting which results in an shell thickness below the required minimum or create contamination traps        Stress corrosion        Sharp indentations, creases, or dents . . .        Dents grater then 6 mm (0.25 inch) to the top third of the tank shell        Dents grater then 10 mm (0.4 inch) to the bottom two thirds of the tank shell        
To comply with the above-listed conditions, a rigorous internal container inspection is required. The inspection may involve not only visual qualitative analyses of the container internal surfaces, but also the actual measurement of possible surface discontinuities, particle sizes, shape of the internal structure, etc. Under today's standard practices, human entry into an inspected vessel is practically inevitable in order to achieve the required inspection quality. That is why the industry accepted and established standard requires a container entry by an inspector through the manway associated with internal container inspections. Thus, the size of a manway, and often its position as well, are regulated to ensure safe entry and exit into and out of a confined space by the inspector.
Another document which establishes requirement for containers shipped around the world has been developed by the UN. For example, UN type T50 Portable ISO Tanks used in International transport for the carriage and use of anhydrous Ammonia UN 1005. These are portable tanks meeting the definition of container in the International Convention for Safe Containers (CSC), 1972, as amended, and are subject to inspection and test in accordance with UN Model Regulations 6.7.3.15 et al. and the CSC. The document imposes strict requirement on conducting container inspections, as well as prescribing stringent time requirements for conducting these inspections. For example, the document states: “ . . . A portable tank may not be filled after expiration of the last 2.5 or 5 year test date. A tank filled within the test date may be transported up to 3 months beyond the date of expiry of the last periodic test date . . . . ” Apparently, containers which have not had the inspection completed on time or have not passed the inspection may not be used for delivery of goods internationally. In the United States, similar regulations developed by DOT. The CSC regulations on container inspection and maintenance are addressed in the CSC regulation #2. For example: “ . . . The first examination must occur no later than 5 years after production and then at least every 2.5 years thereafter . . . . ” In addition, the inspection regulations like CSC specify who may perform the inspection. The presence of qualified and licensed representatives is essential, and only these representatives may perform the inspection and eventually pass or fail the container for further use. The following is also stated in another section of the CSC document: “. . . The inspection and tests described herein must be performed or witnessed by an inspector/agency qualified and approved by the competent authority or its authorized body. The CSC and the UN tank test and inspection may be performed by the same inspector if they are suitably qualified to do so. Typical agencies approved to perform this work are: ABS, Bureau Veritas, Lloyds Register etc . . . . ” In practice, the requirements in the last example demand that a qualified inspector should enter the container and perform the inspection. The final verdict on whether the container may continue to be used in service may be issued only upon completion of the inspection. Unfortunately, none of the qualified inspection agencies are intimately familiar with requirement for containers and systems transporting and supplying HP and UHP products. Therefore, the inspectors may be qualified to perform the inspection of the containers, but they may not be qualified to enter the container transporting HP or UHP goods.
Vessels used to hold and transport bulk quantities of HP and UHP gases and other specialty materials typically include various external valves. The valves can be used for functions such as pressure relief; transfer of material into, out of, and within the vessel, etc. The valves are usually located in a valve box mounted on the shell of the vessel. The valve box helps to protect the valves from damage caused by the valves being struck, crushed, pulled, etc. Moreover, the valve box can be covered so that a blanket of gas can be maintained within the valve box. The gas can be non-contaminating with respect to the material that is held in the vessel, so that infiltration of the gas past the valves and into the interior of the vessel will not contaminate the material within the vessel.
Manways are often integrated with the valve boxes in vessels used to transport bulk quantities of HP and UHP gases and other specialty materials. In particular, the bottom of the valve box is typically secured to a flange or other suitable mating point on the remainder of the valve box by fasteners, so that the bottom of the valve box can be removed to provide access to the internal volume of the vessel.
A valve box that may function as a manway needs to be sufficiently large to facilitate the passage of an adult-sized human therethrough. For example, valve boxes that may function as manways typically have a diameter of at least approximately 2.5 feet. Thus, the interface between the removable bottom of the valve box and the flange or other mating point on the remainder of the valve box is relatively large. Maintaining an airtight seal across such a relatively large interface can be difficult, particularly in transportable vessels that are typically subjected to mechanical shocks, vibrations, and temperature swings during transportation. Thus, leakage across the seal of a manway located at the bottom of a valve box represents a potential source of contamination in a vessel used to hold and transport bulk quantities of HP and UHP gases and other specialty materials.
An ongoing need therefore exists for a substantially leak-free personnel access provision for a vessel used to transport bulk quantities of specialty materials such as HP and UHP gases.